1. Field of the Invention
The present invention relates to a process of and apparatus for molding a thermoplastic sheet and is applicable, e.g., to a blister package used for packaging foods, daily needs, medicines and the like.
2. Description of the Related Art
Recently, the so-called blister package has been employed, in which a resin sheet is molded to have a pocket adapted to the shape of a content of the package, e.g., a medicine and contained it therein and subsequently seals the pocket.
Heretofore, polyvinylchloride (PVC) has been predominantly employed as a material for the above resin sheet. However, polyvinylchloride contains some problems, for example a harmful gas shall be produced when incinerated. Thus, polypropylene (PP) has been employed as a material free from the above problems and having a good moistureproofness instead of polyvinylchloride. In order to achieve high moistureproofness of the resin sheet, a use of a composite material of polypropylene and, e.g., polyvinylidenechloride (PVDC) or polychlorotrifluoroethylene (PCTFE) has been proposed.
The present applicant proposed a polypropylene molding machine providing properties of the resin sheet better than the properties of moldability, molding speed, sealability, curability and half-cuttability of the resin sheet provided by a conventional polyvinylchloride molding machine (See Japanese patent application SHO. 63-231578, which corresponds to U.S. application Ser. No. 07/406,727, filed Sep. 13, 1989). However, when the resin sheet has a multilayered or laminated structure made of a plurality materials instead of a single-layered structure, the laminated resin sheet must be thermally molded at a low temperature since each material of the laminated resin sheet has a different melting point and softening point. Therefore, a conventional high-temperature vacuum molding machine and process for a single-layered resin sheet has failed to attain satisfactory properties such as moldability to a laminated resin sheet.
A prior-art hot plate heating and plug assist compressed air molding machine has been provided as a molding machine which can also mold a laminated resin sheet. This prior-art molding machine can mold a PVC single-layered sheet and PVC/PCD laminated sheet, however, provides poor high-speed moldabilities thereto and a poor moldability to PP. In addition, this prior-art molding machine entails a problem in that it fails to provide a good moldability to a thin resin sheet other than the above problems. In addition, indirect heating and drum vacuum molding machines (See Japanese examined utility model application publications SHO. 60-7131 and SHO. 56-39266, Japanese unexamined patent application publications SHO. 58-126117 and SHO. 58-1261 and the above-referenced Japanese patent application SHO. 63-231578) can mold the PP single-layered sheet and PCV/PVDC laminated sheet but difficultly mold laminated sheets such as a PP/PCTFE/PP laminated sheet and PVC/PCTFE/PP laminated sheet.
An object of the present invention is to provide a process of molding a thermoplastic sheet having a fine molding performance regardless of a sheet structure and material.